Preliminaries 17
directly with the party/entertainment schedule of many students, who tend to study early in
the evening and then amuse themselves until bedtime. It works much better the other way
around.- Sensory memory^17 corresponds to the roughly 0.5 second (for most people) that a sensory
impression remains in the brain’s “active sensory register”, the sensory cortex. It can typically
hold less than 12 “objects” that can be retrieved. It quickly decays and cannot be improved
by rehearsal, although there is some evidence that its object capacity can be improved over a
longer term by practice. - Short term memory is wheresomeof the information that comes into sensory memory is
transferred. Just which information is transferred depends on where one’s “attention” is,
and the mechanics of the attention process are not well understood and are an area of active
research. Attention acts like a filtering process, as there is awealthof parallel information in our
sensory memory at any given instant in time but the thread of our awareness and experience
of time is serial. We tend to “pay attention” to one thing at a time. Short term memory lasts
from a few seconds to as long as a minute without rehearsal, and fornearly all people it holds
4 −5 objects^18. However, its capacity can be increased by a process called “chunking” that
is basically the information compression mechanism demonstrated in the earlier example with
numbers – grouping of the data to be recalled into “objects” that permit a larger set to still
fit in short term memory. - Studies of chunking show that the ideal size for data chunking is three. That is, if you try to
remember the string of letters:
FBINSACIAIBMATTMSN
with the usual three second look you’ll almost certainly find it impossible. If, however, I insert
the following spaces:
FBI NSA CIA IBM ATT MSN
It is suddenly much easier to get at least the first four. If I parenthesize:
(FBI NSA CIA) (IBM ATT MSN)
so that you can recognize the first three are all government agencies in the general category of
“intelligence and law enforcement” and the last three are all marketsymbols for information
technology mega-corporations, you can once again recall the information a day later with only
the most cursory of rehearsals. You’ve taken eighteen ”random”objects that were meaningless
and could hence be recalled only through the most arduous of rehearsal processes, converted
them to six “chunks” of three that can be easily tagged by the brain’s existing long term
memory (note that you arenot learningthe string FBI, you are building anassociationto the
already existing memory of what the string FBImeans, which ismuch easierfor the brain to
do), and chunking the chunks intotwoobjects.
Eighteen objects without meaning – difficult indeed! Thosesameeighteen objectswithmeaning- umm, looks pretty easy, doesn’t it...
Short term memory is still that – short term. It typically decays on atime scale that ranges
from minutes for nearly everything to order of a day for a few things unless the information
can be transferred tolongterm memory. Long term memory is the big payoff –learningis
associated with formation of long term memory.
- umm, looks pretty easy, doesn’t it...
- Now we get to the really good stuff. Long term is memory that you form that lasts a long
time in human terms. A “long time” can be days, weeks, months, years, or a lifetime. Long
(^17) Wikipedia: http://www.wikipedia.org/wiki/memory. Several items in a row are connected to this page.
(^18) From this you can see why I used ten digits, gave you only a few seconds to look, and blocked rehearsal in our
earlier exercise.